Coupled Al/Si and O/N order/disorder in BaYb[Si4–xAlxOxN7–x]sialon

Q2 Chemistry
V. Vinograd, E. Juarez-Arellano, A. Lieb, K. Knorr, W. Schnick, J. Gale, B. Winkler
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引用次数: 0

Abstract

The fractions of aluminium, [Al]/[Al + Si], and oxygen, [O]/[O + N], in crystallographically distinct sites of BaYb[Si4–xAlxOxN7–x] oxonitridoaluminosilicate (space group P63mc, No. 186) were refined based on the results of neutron powder diffraction for a synthetic sample with the composition of x = 2.2(2) and simulated as functions of temperature for the compositions x = 2 and x = 2.3 using a combination of static lattice energy calculations (SLEC) and Monte Carlo simulations. The SLEC calcu lations have been performed on a set of 800 structures differing in the distribution of Al/Si and O/N within the 2 × 2 × 2 supercell containing 36 formula units of BaYb[Si4–xAlxOxN7–x]. The SLEC were based on a transferable set of empirical interatomic potentials developed within the present study. The static lattice energies of these structures have been expanded in the basis set of pair-wise ordering energies and on-site chemical potentials. The ordering energies and the chemical potentials have been used to calculate the configuration energies of the oxonitridoaluminosilicates (so-called sialons) using a Monte Carlo algorithm. The simulations suggest that Al and O are distributed unevenly over two non-equivalent T(Si/Al) and three L(N/O) sites, respectively, and the distribution shows strong dependence both on the temperature and the composition. Both simulated samples exhibit order/disorder transitions in the temperature range 500–1000 K to phases with partial long-range order below these temperatures. Above the transition temperatures the Si/Al and N/O distributions are affected by short-range ordering. The predicted site occupancies are in a qualitative agreement with the neutron diffraction results.
BaYb[si4 - xalxn7 - x]硅氧烷中Al/Si和O/N的有序/无序耦合
铝的分数,(Al) / (Al + Si)和氧气,[O] / [O + N],在结晶学不同的网站BaYb [Si4-xAlxOxN7-x] oxonitridoaluminosilicate(空间P63mc组186号)精制结果的基础上对合成样品的中子粉末衍射,x = 2.2(2)的构成和模拟温度的函数组成x = 2和x = 2.3使用静态的结合晶格能的计算(SLEC)和蒙特卡罗模拟。SLEC计算在含有BaYb[Si4-xAlxOxN7-x] 36个公式单位的2 × 2 × 2超级单体中,对800个Al/Si和O/N分布不同的结构进行了计算。SLEC是基于本研究中开发的一套可转移的经验原子间势。这些结构的静态晶格能被扩展为成对有序能和现场化学势的基集。利用有序能和化学势,用蒙特卡罗算法计算了氧化氮铝硅酸盐(所谓的sialons)的构型能。模拟结果表明,Al和O分别在两个非等效的T(Si/Al)和三个L(N/O)位点上分布不均匀,且分布与温度和成分有很强的相关性。两种模拟样品在500-1000 K的温度范围内都表现出有序/无序转变,到低于这些温度的部分长程有序相。在过渡温度以上,Si/Al和N/O分布受短程有序影响。预测的占位率与中子衍射结果在定性上是一致的。
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来源期刊
CiteScore
1.47
自引率
0.00%
发文量
0
审稿时长
3 months
期刊介绍: Zeitschrift für Kristallographie International journal for structural, physical, and chemical aspects of crystalline materials ISSN 0044-2968 Founded in 1877 by Paul Groth Zeitschrift für Kristallographie is one of the world’s oldest scientific journals. In original papers, letters and review articles it presents results of theoretical or experimental study on crystallography.
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